A powerboat is going at 80 km h–1 when its motor is turned off. In 5.0 seconds its velocity decreases to 50 km h–1. The boat and its passengers weigh 1 tonne.
Calculate the average force exerted on the boat by the combined drag of the air and the water.
MY ANSWER:
p1 = mv
= (1000)(1.3x10^3)
= 1.3x10^6 Kgms^-1
p2 = (1000)(0.83x10^3)
= 0.83x10^6 kgms^-1
Δp = (0.83x10^6) - (1.3x10^6)
= -0.47x10^6
F = Δp/Δt
= (-0.47x10^6)/5
= -94000N
and the answer is -1700N????
Calculate the average force exerted on the boat by the combined drag of the air and the water.
MY ANSWER:
p1 = mv
= (1000)(1.3x10^3)
= 1.3x10^6 Kgms^-1
p2 = (1000)(0.83x10^3)
= 0.83x10^6 kgms^-1
Δp = (0.83x10^6) - (1.3x10^6)
= -0.47x10^6
F = Δp/Δt
= (-0.47x10^6)/5
= -94000N
and the answer is -1700N????
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I think you have calculated your speeds wrong....
80km/h is 22.2m/s - you have only divided by 60 (giving m/min)
80km/h is 22.2m/s - you have only divided by 60 (giving m/min)